Py3: Replace six.moves imports

Replace six.moves and six.StringIO/BytesIO imports with cannonical
Python 3 packages.

Note: six.moves.input behaves differently than builtin input function.
Therefore I left six.moves.input for now.

See: https://pagure.io/freeipa/issue/7715
Signed-off-by: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Fraser Tweedale <ftweedal@redhat.com>

ipaplatform/redhat/tasks.py

@@ -31,6 +31,7 @@ import os
 import socket
 import traceback
 import errno
+import urllib
 import sys
 
 from ctypes.util import find_library
@@ -38,7 +39,6 @@ from functools import total_ordering
 from subprocess import CalledProcessError
 
 from pyasn1.error import PyAsn1Error
-from six.moves import urllib
 
 from ipapython import directivesetter
 from ipapython import ipautil